1. Field of the Invention
The present invention relates to an air conditioner having a hot gas bypass function of heating air when a gas refrigerant of high temperature and pressure, which has been discharged from a refrigerant compressor, is decompressed and introduced into a refrigerant evaporator and the refrigerant evaporator is used as a radiator from which the heat of the gas refrigerant is radiated. More particularly, the present invention relates to an air conditioner for vehicle use which is preferably mounted on a vehicle.
2. Description of the Related Art
In a conventional air conditioner for vehicle use, warm water (engine coolant) is circulated in a heat exchanger used for heating in winter, and air to be conditioned is heated by this heat exchanger for heating while the warm water is used as a heat source. In this case, when the temperature of the warm water is low, air at low temperature is blown out into a passenger compartment, that is, it is impossible to provide a sufficiently large heating capacity.
In order to solve the above problems, conventionally, an air conditioner is proposed in which the heating capacity is exhibited by providing a hot gas bypass. In this conventional air conditioner, when the temperature of warm water is low in the case of starting an engine, gas refrigerant (hot gas) compressed by a compressor in the refrigerating cycle is introduced into an evaporator which bypasses a condenser, and heat is emitted from the gas refrigerant to air to be conditioned by the evaporator, so that a heating function can be exhibited. However, the hot gas cycle in which gas refrigerant of high temperature and pressure in the refrigerating cycle is used, the heating capacity is greatly affected by whether or not a sufficiently large quantity of refrigerant is charged into the air conditioner. For example, when a sufficiently large quantity of refrigerant is not charged, the heating capacity is lowered, and when an excessively large quantity of refrigerant is charged, the compressor is too frequently turned on and off, and the durability of the magnet switch of the compressor is deteriorated.
In order to solve the above problems, Japanese Unexamined Patent Publication No. 5-272817 discloses the following techniques. A high pressure on the discharging side of the compressor is detected, and it is judged whether a quantity of circulating refrigerant is sufficient or insufficient in the heating mode conducted by the hot gas bypass. In the case where the quantity of refrigerant is too large, the refrigerant is discharged onto the condenser side. In the case where the quantity of refrigerant-is too small, the residing refrigerant is recovered from the condenser side. Recovery of the residing refrigerant is specifically conducted in such a manner that the entry side of the condenser is opened and the entry side of the hot gas bypass path is closed, that is, the air conditioner is set in the normal cooling mode, and then the compressor is operated.
However, in the heating mode conducted by the hot gas bypass, high pressure on the discharging side of the compressor fluctuates by factors such as a heat load in the cycle, rotary speed of the compressor, throttle diameter of the decompression means in the hot gas bypass path and so forth. Therefore, it is difficult to appropriately judge only by the high pressure whether the quantity of refrigerant is sufficient or insufficient.
In addition to that, after the hot gas bypass operation has been started, in order to stabilize the operation of high pressure, it takes a long time. At least 5 minutes is required to stabilize the operation at high pressure. In this period of time, the heating capacity is insufficient due to lack of the refrigerant. Further, a sufficiently large quantity of oil is not returned to the compressor, which causes a failure of lubrication of the compressor.
When the residing refrigerant is recovered in the case of heating in winter, the outside temperature is low and a heat load for cooling is very light. Therefore, a difference between high and low pressure in the refrigerating cycle is very small. For the above reasons, in the case where a variable displacement type compressor, in which a displacement of the compressor is changed by utilizing a difference between high and low pressure in the refrigerating cycle, is used for the compressor, the displacement is not increased, that is, the displacement is kept small because the difference between high and low pressure in the refrigerating cycle is small. Accordingly, it becomes impossible to recover the residing refrigerant.
In order to solve the above problems, the present applicant has proposed the refrigerating cycle disclosed in U.S. Pat. No. 6,105,375. In this conventional refrigerating cycle device, when the heating mode conducted by the hot gas bypass is started, when the compressor is operated while both the entry side of the condenser and that of the hot gas bypass path are closed, the residing refrigerant existing on the condenser side is forcibly recovered onto the evaporator side.
However, in the case where recovery control of recovering the residing refrigerant is conducted as described above, as the compressor is continuously driven under the condition that only a small quantity of refrigerant and oil exist in the hot gas cycle, it becomes impossible to supply a necessary quantity of oil to the compressor for a long period of time. In this case, failure of lubrication is caused in the compressor, which leads to abrasion or breakdown of parts of the compressor. In the worst case, the compressor is locked.
Conventionally, in the case where hot gas bypass operation is conducted for more than a predetermined period of time, there is a possibility that refrigerant leaks from the electromagnetic valve to the condenser side. In this case, the quantities of refrigerant and oil in the hot gas cycle are decreased, and the hot gas capacity is lowered and, further, abrasion of the compressor is caused due to a reduction in the quantity of oil circulated.